Place apples and water in a large saucepan. Bring to the boil, reduce heat, and cook for 25 minutes, stirring occasionally. Add more water as necessary to keep simmering.

Wrap mustard seeds in muslin or cheesecloth, and place with apples. Mix tomatoes, onions, garlic, sultanas, sugar, curry powder, cayenne pepper, salt and vinegar in with the apples. Stir until sugar has dissolved.